A valve assembly for use with a self-sealing collapsible storage bag, the valve assembly having a first portion comprising a housing that has a sealing surface and contains a valve mechanism. The compressor system includes two piston assemblies that are coaxially coupled to one another, and that are of differing cross sectional areas. Absorbed biomolecules can be eluted or recovered from the substrate at a future time, and optionally be subjected to a subsequent analysis or application.